The present invention relates to rotary machinery and has as an object the reduction of noise in the operation of certain types thereof.
Machines of the kind having a component close to a rotor can be noisy in operation if the arrangement is such that the component and the rotor can act on the atmosphere in the region of the component to disturb said atmosphere and thereby produce noise having fundamental frequency proportional to the rate of rotation of the rotor relative to the component. Such noise, produced by disturbance of the atmosphere, is to be distinguished from noise produced by solid-to-solid impact. It is considered that machines which produce such noise will be readily recognizable by those who have been alerted to the possibility of its occurrence.